2 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 123 



with a surface area of 0.2 square kin and a maximum depth of 31.5 m 

 (Roth and Neff, 1964, pp. 5, 8). Of these, collections were made 

 only in Mountain Lake. 



The streams vary in size from tiny spring rills cascading over 

 rocky and sandy bottoms to the 161-meter-wide New River, which 

 courses with a moderate current over bedded limestone and discharges 

 from 1186 to 35,228 cubic feet per second at the Eggleston Gauging 

 Station (average annual minimum and flood flows from 1930 to 1958) 

 (Ross and Perkins, 1959, p. 6). 



In much of the area, sandstones of the Silurian Age overlie 

 Ordovician limestones and shales, and at higher elevations the waters 

 flowing over the exposed sandstones have a total hardness of as little 

 as 4 ppm. Some streams at lower elevations, passing over and through 

 channels in calciferous rocks, accumulate soluble carbonates to the 

 extent that in the larger valley streams the total hardness may attain 

 concentrations of as much as 142 ppm (Shoup, 1948). In one stream 

 (sta. 85) the M.O. alkalinity reaches 350 ppm. 



The midsummer temperature of one of the springs (sta. 68) located 

 at an elevation of 1219 m is 13° C, and that of the valley streams 

 may rise to 26.7° C (Shoup, 1948). 



Physiographic, hydrographic, and ecological data for several of 

 the streams sampled in this study may be found in Burton and Odum 

 (1945), Ross and Perkins (1959), and Shoup (1948). 



Precise numbers of specimens examined during the course of the 

 survey are not available; however, records include some 2700 

 crayfishes, 5200 ostracods, and 1600 branchiobdellids. 



Collection techniques and disposition of specimens. — This 

 study was initiated during the summer of 1960 and collections have 

 been amassed during each of the succeeding summers through 1965. 

 One hundred and twenty-seven stations (see map 1) were established 

 in the area, and collections of the crayfishes were made by hand from 

 open water or burrows and with the aid of minnow seines. In most 

 instances all of the crayfishes collected from one station on a given 

 day were killed in 6 to 10 percent formalin in a single container. In 

 the laboratory, the ostracods and branchiobdellids were recovered 

 from the bottom of the container and prepared for identification. 

 All of the species (crayfish, ostracods, and branchiobdellids) found 

 in that collection were considered to be associated and were so 

 recorded. In instances wherein there was a question as to whether 

 or not a particular ostracod species actually lived upon the exoskeleton 

 of a particular species of crayfish, that species of crayfish was recol- 

 lected, preserved alone, and the ostracods recovered from that 

 collection were then known as associates. In that manner it was 

 determined that the assumed associations were highly probable. In 

 order to determine the abundance and distribution of certain sym- 



